Method for fast roaming in a wireless network

ABSTRACT

A roaming service method for a fast and secure wireless network is provided. In an embodiment of the present invention, an AP, which an STA associates with, transmits proactive keys needed for roaming to neighbor APs of the AP. When the STA moves to one of the neighbor APs, a reassociation is carried out between the STA and the neighbor AP using the already provided proactive key. In another embodiment of the present invention, an authentication server transmits proactive keys needed for roaming to neighbor APs to which the STA is likely to move, so that when the STA moves to one of the neighbor APs, a reassociation is carried out between the STA and the neighbor AP using the already provided proactive key.

PRIORITY

This application is Continuation of U.S. application Ser. No.10/752,675, filed on Jan. 8, 2004, which claims priority under 35 U.S.C.§ 119 to an application entitled “Method for Fast Roaming in a WirelessNetwork” filed in the U.S. Patent and Trademark Office on Jan. 14, 2003and assigned Ser. No. 60/439,891, the contents of which are incorporatedherein by reference.

GOVERNMENT RIGHTS

This invention was made with Government support under Contract No.60NANB1D0113 awarded by the National Institute of Standards andTechnology, and under Contract No. MDA90402C0428 awarded by the NationalSecurity Agency. The U.S. Government has certain rights in theinvention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a roaming service in a fastand secure wireless network, and in particular, to a method of providinga security key to minimize time required for a roaming service.

2. Description of the Related Art

A LAN (Local Area Network) is a collection of personal terminals, mainframes, and workstations which share a common communication linkgenerally within a range of 300 m. The LAN is a fast communicationnetwork built within a distance that allows an accurate transfer ofcurrent or signals between the personal terminals. For example, the LANprovides connectivity to equipment within an office building so thatworkers can efficiently share the information contained on theequipment. In its initial developmental stage, the LAN usually adoptedas its communication link a wired network that directly transferselectrical signals. Along with the development of wireless protocols, awireless network has substituted for the wired network. A LAN using awireless network is called WLAN (Wireless LAN) or in-building wirelessnetwork. One WLAN is based on IEEE 802.11 and proposed by the U.S. IEEE(International Electric and Electronic Engineers) group. IEEE802.11-based WLAN has seen rapid growth and deployment in the recentyears. Owing to convenient network connectivity, the widespreaddeployment of the WLAN in the future is easily predicted. To meetincreasing demands for a very high-speed wireless Internet, existingWLAN systems emerge as a foundation for a fast wireless public network.The WLAN attracts more attention because of the expectations that theWLAN provides a high speed link which mobile communication systems donot and guarantees secure communications for WLAN users owing to therapid development of WLAN security technology. Therefore, the WLANsecurity technology as well as the increase of data rate is asignificant task to achieve for the WLAN systems.

The IEEE 802.11 network MAC (media access control) specification allowsfor two operating modes, namely, ad hoc and infrastructure. In the adhoc mode, two or more wireless stations (STAs) recognize each other andestablish a peer-to-peer communication without any existinginfrastructure, whereas in the infrastructure mode, there is a fixedentity referred to an access point (AP) that bridges all data betweenthe STAs associated with it. An AP and associated STAs form a basicservice set (BSS) communicating on the unlicensed RF (Radio Frequency)spectrum.

FIG. 1 illustrates the configuration of a typical WLAN that supports theinfrastructure mode.

Referring to FIG. 1, a plurality of APs 120 a and 120 b are connectedvia a single distributed system (DS) 110. The DS 110 is a wired networkand establishes a communication link between the APs 120 a and 120 b.Each of the APs 120 a and 120 b forms a predetermined service area andbridges between the DS 110 and STAs 130 a and 130 b (or 130 c and 130 d)within its service area. As mentioned before, an AP and associated STAsform a BSS and a service is provided on a BSS basis. A collection of theAPs 120 a and 120 b can extend the BSSs to an extended service set(ESS). The STAs 130 a to 130 d authenticate to their respective APs 120a and 120 b to access the WLAN system. In other words, the STAs 130 a to130 d are allowed to access the network only by an authenticationprocedure. The authentication involves transfer of state information.The state information contains a key (hereinafter, referred to as asecurity key) that provides security between the DS and the STA orbetween the AP and the STA.

As stated above, to communicate with the DS via a particular AP, an STAneeds a security key. Hereinbelow, a process of assigning a security keyis defined as authentication. The authentication procedure involvesencryption key distribution and an encryption algorithm to encryptwireless data.

The IEEE 802.11 standard regulates that data is encrypted by a WEP(Wired Equivalent Privacy) algorithm and the encryption key is sharedpreliminarily and used as fixed. For details, see “ISO/IEC, “WirelessLAN Medium Access Control (MAC) and Physical layer (PHY)specifications,” ISO/IEC 8802-11, ANSI/IEEE Std 802.11, 1999”.

To correct wireless security flaws of the IEEE 802.11-based WLANsystems, IEEE 802.111 specifies IEEE 802.11x/1aa-based access control,security session management, dynamic key exchange and key management,and application of a new symmetric key encryption algorithm forprotection of wireless data. IEEE 802.1X/1aa provides a framework foruser authentication and key exchange, whereas IEEE 802.11i regulatesthat IEEE 802.1X/1aa can be used as a comprehensive framework for userauthentication and key exchange. IEEE 802.11i further defines 4-wayhandshake as a key exchange method, key hierarchy, and new ciphersuites.

FIG. 12 is a view illustrating a signal flow for WLAN security accessbased on IEEE 802.1X/1aa and IEEE 802.11i. As noted from FIG. 12, IEEE802.11 access, IEEE 802.1X authentication, IEEE 802.11i key exchange,and IEEE 802.1aa authentication must be connected to one another toauthorize connection to an external network via an AP throughauthentication and key exchange.

FIG. 2 illustrates a hierarchy of security keys for the typical WLAN.Referring to FIG. 2, the security keys include a master key (MK), apairwise master key (PMK), and a pairwise transient key (PTK). Ahigher-layer server, an AAA (Authentication, Authorization andAccounting) server in the DS derives the PMK from the MK and provides itto an STA via an AP to which the STA has connectivity. The AP and theSTA generate the PTK from the PMK. The MK, already known to the STA aswell as the AAA server, provides security between the STA and the AAAserver. The PTK provides security between the STA and the AP. The PTKserves as a key confirmation key (KCK), a key encryption key (KEK), anda temporal key. Bits 0-127 of the PTK are assigned to the KCK, bits 128to 255 to the KEK, and the remaining bits to the temporary key.

FIG. 3 illustrates an example of key assignment to each component in thetypical WLAN. The key assignment presupposes that a new STA 340 attemptsto access a first AP 320 (AP1). Referring to FIG. 3, an AAA server 310generates a PMK from a known MK upon request for key assignment from theSTA 340 and transmits it to AP1. AP1 in turn provides the PMK to the STA340 and derives a PTK from the PMK. The STA 340 also generates the PTKfrom the PMK. Hence, the STA 340 knows the MK, PMK and PTK. A RADIUS(Remote Authentication Dial-In User Service) server is generally used asthe AAA server 310.

Because of the mobility-enabling nature of the WLAN having theconfiguration illustrated in FIG. 1, the STA can move from a prior-AP toa new-AP. To continue an on-going service provided by the prior-AP, aroaming service is needed for the STA. The AP to which the STA hadphysical layer connectivity is referred to as the prior-AP orcurrent-AP, while the AT to which the STA gets physical layerconnectivity after roaming is referred to as the new-AP.

The roaming process refers to the mechanism or sequence of messagesexchanged between APs and an STA. To continue an on-going service in thenew-AP after roaming, the STA needs an additional security key,accurately speaking, another PMK.

The complete roaming process can be divided into two distinct logicalsteps: discovery and re-authentication as described below.

1. Discovery: Attributing to mobility, the signal strength and thesignal-to-noise ratio of the signal from an STA's current AP mightdegrade and cause it to loose connectivity and to initiate a handoff. Atthis point, the STA might not be able to communicate with its current AP(prior-AP). Thus, the STA needs to find potential APs in range topotentially associate with. This is accomplished by a MAC layer scanfunction. During a scan, the STA listens for beacon messages sent outperiodically by APs at a rate of 10 ms on assigned channels. Thus theSTA can create a list of APs prioritized by the received signalstrength.

There are two kinds of scanning methods defined in the standard: activeand passive. As the names suggest, in the passive mode, the STA searchesfor the potential APs simply by listening for beacon messages. In theactive mode, apart from listening to beacon messages, the STA sendsadditional probe broadcast packets on each channel and receivesresponses from APs. Thus, the STA actively probes for the APs.

2. Re-authentication: The STA attempts to reauthenticate to an APaccording to the priority list. The re-authentication process typicallyinvolves an authentication and a reassociation to the new-AP. There-authentication phase involves the transfer of a security key from theprior-AP. This can be achieved through an IAPP (Inter Access PointProtocol). The re-authentication process can be divided into theauthentication phase and the reassociation phase.

FIG. 4 illustrates a re-authentication procedure performed by an EAP-TLSprotocol for a roaming service in a conventional WLAN. In theillustrated case, it is assumed that an STA 440 moves from AP_A 420 toAP_B 430. Thus AP_A 420 is a prior-AP and AP_B 430 is a new-AP.Referring to FIG. 4, the STA 440 recognizes that AP_B 430 exists as aneighbor AP in the discovery phase and then requests from AP_A 420 asecurity key by which to communicate with AP_B 430. AP_A 420 requeststhe security key from an AAA server 410 via AP_B 430. The AAA server 410generates a new PMK and provides it to AP_B 430. AP_B 430 stores the PMKand provides it to AP_A 420. AP_A 420 in turn provides the PMK to theSTA 440. Thus the STA 440 and AP_B 430 can create a PTK from the PMK.When the STA 440 moves to AP_B 430, it can maintain an on-going serviceusing the PTK.

As described above, in the conventional roaming process, the STA movesfrom the current AP, scans all potential APs, and associates with an APhaving the highest RSSI (Received Signal Strength Indicator). Theassociation procedure starts with requesting a PMK for the new-AP andends with creating a PTK from the PMK.

Accordingly, the conventional roaming process involves probe delay inthe discovery phase, and pre-authentication delay in there-authentication phase.

1. Probe Delay: Messages from an active scan for roaming are referred toas probe messages. The latency for this process is called probe delay.The STA transmits a probe request message and waits for responses fromAPs on each channel. Probe wait latency is defined as the time the STAwaits on one particular channel after sending the probe request. This ismeasured as the time difference between subsequent probe requestmessages. Thus according to the above procedure, the traffic on thechannel and the timing of probe response messages affect the probe-waittime.

2. Pre-Authentication Delay: This is the latency incurred during theexchange of re-authentication frames. Pre-authentication consists of twoor four consecutive frames depending on the authentication method usedby the AP. The pre-authentication delay has been described withreference to FIG. 4.

As described above, the conventional WLAN involves various delays duringroaming of an STA. As a result, a total roaming time is extended to 1 to13 seconds. This implies that communication disconnection from the STAis lengthened, which may adversely affect service quality. Even fastroaming may be impossible when the STA fails to receive a security keyfor communication with the new AP from the current AP.

SUMMARY OF THE INVENTION

An object of the present invention is to substantially solve at leastthe above problems and/or disadvantages and to provide at least theadvantages below. Accordingly, an object of the present invention is toprovide a method of minimizing delay involved in a roaming process.

Another object of the present invention is to provide a roaming servicemethod for precluding the effects of the security system of a prior-APon that of a new-AP even if the security system of the prior-AP isimpaired.

A further object of the present invention is to provide a method ofproviding neighbor APs with security keys needed for roaming by asecurity caching technique.

Still another object of the present invention is to provide a method ofacquiring security keys for neighbor APs using a security key used foran AP which an STA is currently associated with and providing thesecurity keys to the neighbor APs.

Still further object of the present invention is to provide a method ofproviding security keys to neighbor APs using an AP-neighborhood graphmanaged by an AP, which an STA is currently associated to.

Yet another object of the present invention is to provide a method ofdistributing security keys to APs neighboring an AP which an STA iscurrently associated with in an authentication server.

Yet further object of the present invention is to provide a method ofmanaging an AP-neighborhood graph to distribute security keys to APsneighboring a current AP, which an STA is currently associated to in ahigher-layer server.

Yet still another object of the present invention is to provide a methodof performing a roaming process between a neighbor AP and an STA using asecurity key distributed to the neighbor AP before the roaming process.

The above objects are achieved by providing a roaming service method fora fast and secure wireless network.

According to one aspect of the present invention, in a wireless network,having at least two APs, each AP having a predetermined service area,and an STA that receives a communication service by associating with afirst AP being one of the at least two APs, to support a roaming servicefor the STA, the first AP generates an AP-neighborhood graph withneighbor APs to which the STA is likely to move, acquires security keysfor the respective neighbor APs based on association information gainedfrom the association of the STA to the first AP, and transmits thesecurity keys to the respective neighbor APs by security caching. Thus,a pre-authentication is performed such that when the STA attempts toroam to one of the neighbor APs, fast roaming is provided via a securitykey provided to the neighbor AP.

According to another aspect of the present invention, in a wirelessnetwork having at least two APs, each AP having a predetermined servicearea, and an STA that receives a communication service by associatingwith a first AP being one of the at least two APs, to support a roamingservice for the STA, a neighbor AP of the first AP, which is managed byan AP-neighborhood graph drawn for the first AP, receives a security keyfrom the first AP by security caching from among security keys generatedby the first AP for respective neighbor APs using associationinformation gained from the association of the STA to the first AP, andperforms fast roaming using the security key when the STA attempts toroam to the neighbor AP.

According to a further aspect of the present invention, in a wirelessnetwork having at least two APs, each AP having a predetermined servicearea, and an STA that receives a communication service by associatingwith a first AP being one of the at least two APs, to support a roamingservice between the first AP and a neighbor AP of the first AP, managedby an AP-neighborhood graph drawn for the first AP, security keys areacquired for respective neighbor APs based on association informationand transmits the security keys to the respective APs by securitycaching. Here, the association information is gained by the first APfrom the association of the STA to the first AP. The neighbor APreceives a security key from the first AP and performs fast roamingusing the security key when the STA attempts to roam to the neighbor AP.

According to the first three aspects of the present invention, it ispreferred that the association information includes a PMK and an RK,which are acquired by the first AP, and the MAC addresses of the STA andthe neighbor APs.

According to still another aspect of the present invention, in awireless network having at least two APs, each AP having a predeterminedservice area, an STA that receives a communication service byassociating with a first AP being one of the at least two APs, anauthentication server (AS) that authenticates the STA, and an accountingserver that provides billing for the STA, to support a roaming servicefor the STA, the accounting server generates an AP-neighborhood graphfor the first AP to manage neighbor APs to which the STA is likely tomove from the first AP. When the first AP reports to the accountingserver completed association of the STA to the first AP, the accountingserver notifies the neighbor APs of the association. Each of theneighbor APs requests a security key to the AS in response to thenotification from the accounting server. The AS generates a security keyfor each of the neighbor APs based on association information from theassociation of the STA to the first AP in response to the request andtransmits the security key to each of the neighbor APs. When the STAattempts to roam to one of the neighbor APs, a neighbor AP, to which theSTA is to form a connection, performs a pre-authentication, so that fastroaming can be carried out using the security key provided to theneighbor AP.

According to the fourth aspect of the present invention, it is preferredthat the association information includes an MK, a PMK assigned to thefirst AP, and the MAC addresses of the STA and the neighbor APs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 illustrates the configuration of a typical WLAN as an example ofa wireless network;

FIG. 2 illustrates a hierarchy of security keys in the typical WLAN;

FIG. 3 illustrates an example of key assignment to each component in thetypical WLAN;

FIG. 4 illustrates assignment of a security key needed for roaming in aconventional WLAN;

FIGS. 5A and 5B illustrate AP-neighborhood graph generation according tothe present invention;

FIG. 6 illustrates an example of a roaming path in which an STA roams,referred to for describing the present invention;

FIG. 7 illustrates generation of security keys according to anembodiment of the present invention;

FIGS. 8A, 8B and 8C illustrate a roaming process according to theembodiment of the present invention;

FIG. 9 is a diagram illustrating signaling in the roaming processaccording to the embodiment of the present invention;

FIGS. 10A to 10E illustrate a roaming process according to anotherembodiment of the present invention;

FIG. 11 illustrates an example of PMKs generated for a particular STAroam pattern;

FIG. 12 is a diagram illustrating signaling for initial association inthe typical WLAN;

FIG. 13 is a diagram illustrating signaling before roaming according tothe second embodiment of the present invention;

FIG. 14 is a diagram illustrating signaling after roaming according tothe second embodiment of the present invention; and

FIG. 15 is a graph comparing experiment results for a conventionalroaming scheme (full authentication) and a roaming scheme of the presentinvention (re-authentications).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, well-known functions or constructions are not described indetail since they would obscure the invention in unnecessary detail.

Three schemes can be considered to support fast roaming in a WLAN.

First, APs each preserve all necessary security keys for roaming. EachAP reserves memory space for the roaming service, stores all securitykeys needed for the roaming service in the memory, and retrieves onesecurity key from the memory when necessary. A distinctive shortcomingof this scheme is the requirement of a large-capacity memory.

A second scheme is to provide neighbor APs with necessary security keysfor roaming by security caching accomplished by the IAPP protocol. To doso, each AP manages information about its neighbor APs using anAP-neighborhood graph. Also, the AP generates security keys for theneighbor APs using a known security key and provides the generatedsecurity keys to the neighbor APs by the security caching.

The third scheme is that a higher-layer server (accounting server)manages neighbor APs for each AP and provides the neighbor APs withsecurity keys necessary for roaming when an STA accesses the AP. Toimplement this scheme, the higher-layer server is provided to manage theAP-neighborhood graph for each AP. The higher-layer server may be anexisting AAA server or a separately procured server. Depending on theamount of information regarding the managed AP-neighborhood graphs, aplurality of higher-layer servers can be used.

The above-described second and third schemes are implemented as firstand second embodiments of the present invention. These embodimentscommonly require the AP-neighborhood graph by which neighbor APs aremanaged for each AP. They differ in that each AP manages itsAP-neighborhood graph in the first embodiment, while a higher-layerserver manages its AP-neighborhood graph in the second embodiment. Inthe embodiments of the present invention, the process of providingpotential APs with security keys needed for roaming is further included.The AP-neighborhood graph is required in both embodiments since thepotential APs are a set of APs to which an STA may move. TheAP-neighborhood graph defines connections between an STA and itspotential APs, which the STA may be associated with by roaming. Hence,before detailing the embodiments of the present invention, the processof how the AP-neighborhood graph is created will first be described.

1. Generation of AP-Neighborhood Graph

The AP-neighborhood graph required to implement the present inventioncan be generated based on the locations of APs in a WLAN. Becausepotential APs are different for each AP, an AP-neighborhood graph iscreated for each AP. This is done in three methods. One of them is thatan administrator manually generates AP-neighborhood graphs forindividual APs based on the locations of the APs and registers them.Each time a change is made to the AP layout, the administrator updatesthe AP-neighborhood graphs. Another method is that initialAP-neighborhood graphs are registered by the administrator andautomatically updated each time the AP layout is changed.

The third method is that the AP-neighborhood graph is automaticallygenerated for each AP and automatically updated each time the AP layoutis changed. According to this method, however, roaming is carried out bythe conventional roaming process until the AP-neighborhood graph isgenerated. In other words, a procedure for checking connections to eachAP is needed. For example, if an STA associated to AP_A attempts toinitially roam to AP_B that the STA has never moved to, AP_B performs anIAPP procedure to receive a context corresponding to the STA from AP_A.AP_A and AP_B then confirm that there is a connection between them forroaming and thus can update their AP-neighborhood graphs. After theupdating, the STA can roam from AP_A to AP_B or vice versa without theIAPP procedure.

The physical path and distance between APs are considerations to takeinto account when constructing an AP-neighborhood graph in any of theabove methods. To draw a connection between APs in an AP-neighborhoodgraph, there must exist a physical connection between the APs withoutpassing through any other AP. Also, the distance between the physicallyconnected APs should not exceed a threshold. As a matter of fact, theSTA would perform an initial procedure for establishing a communicationwith a nearby AP rather than roam to a remote AP.

An example of an AP-neighborhood graph will be shown below.

FIG. 5A illustrates an example of an AP layout in a WLAN to which thepresent invention is applied and FIG. 5B illustrates an AP-neighborhoodgraph constructed based on the AP layout.

Referring to FIG. 5A, AP_C is located in a closed space with oneentrance. Thus AP_B is the only AP to which an STA can move from AP_C.This implies that roaming only to AP_B is allowed for the STA in AP_C.Meanwhile, an STA in AP_B can move to any of AP_A, AP_D, AP_E and AP_Cbecause corridors (physical connections) run from AP_B to these APs.That is, the STA is free to roam from AP_B to all APs illustrated inFIG. 5A. If the STA is located in AP_A, it can only move to AP_B or AP_Ewithout passing through any other AP. Hence, the STA can roam from AP_Ato AP_B or AP_E. AP_E is directly connected to all APs except AP_C, sothat an STA in AP_E can roam to any of the APs other than AP_C. Directroaming for an STA from AP_D is confined to AP_B and AP_E. Roaming fromAP_A to AP_D, or from AP_D to AP_A, is not allowed due to a longdistance between them. Instead of roaming, the STA reassociates to AP_Bbefore it roams to AP_D or AP_A.

Referring to FIG. 5B, the illustrated AP-neighborhood graph shows all ofthe connections among the APs in the WLAN. Yet, the above-describedsecond neighborhood graph generation method is viable as long as each APhas knowledge of potential APs to which it may have connectivity. Forexample, knowledge of AP_B and AP_E as potential APs is substantiallysufficient for AP_A and knowledge of AP_A, AP_C, AP_D and AP_E aspotential APs is substantially sufficient for AP_B. On the other hand,in the third neighborhood graph generation method, an accounting servermanages an AP-neighborhood graph for each AP.

As mentioned earlier, the AP-neighborhood graph is manually generated bythe administrator or automatically generated by the conventional handoffprocedure.

In the case where each AP automatically generates an AP-neighborhoodgraph, upon receipt of a reassignment request message from an STA, theAP determines whether a temporarily stored context corresponding to theSTA exists. The AP is a new-AP for the STA. If the context exists, itmeans that the AP has already created an AP-neighborhood graphcontaining a prior-AP to which the STA had connectivity. On thecontrary, if the context is absent, it means that connectivity to theprior-AP has not yet been defined in the AP-neighborhood graph. Thenew-AP then receives the context corresponding to the STA from theprior-AP by the conventional IAPP procedure and updates theAP-neighborhood graph so that a connection line is drawn between thenew-AP and the prior-AP in the AP-neighborhood graph.

In this manner, the AP-neighborhood graph is generated in the firstembodiment of the present invention characterized by management of theAP-neighborhood graph at each AP. Meanwhile, in the second embodiment ofthe present invention, since a higher-layer server manages anAP-neighborhood graph for each AP, when a new connection is established,a corresponding AP reports the new connection to the higher-layer serverso that the AP-neighborhood graph of the AP can be updated with thelatest information. It is also possible that if an STA roams to anew-AP, the higher-layer server updates an AP-neighborhood graph for aprior-AP by adding the new-AP to the graph as a neighbor AP of theprior-AP.

2. First Embodiment

An AP generates PMKs for neighbor APs managed in its AP-neighborhoodgraph and transmits the PMKs to the neighbor APs using a securitycaching technique accomplished by the IAPP protocol. When an STA roamsto one of the neighbor APs, a security system operates based on the PMKprovided to the neighbor AP, thereby enabling fast roaming.

The security caching technique refers to a scheme in which each APrecognizes potential APs that it may get connectivity to by itsAP-neighborhood graph, generates PMKs for the potential APs, andtransmits the PMKs to the neighbor APs. Therefore, re-authenticationlatency involved in the roaming process is minimized. The securitycaching technique is based on a locality of mobility principle. In thisenvironment, an STA association pattern is the sequence of APs that theSTA becomes associated with in a given interval of time.

The first embodiment of the present invention will be detailed withreference to the attached drawings. It is assumed herein that each APmanages its own AP-neighborhood graph.

FIG. 6 is a view conceptually illustrating a roaming process by thesecurity caching technique according to the present invention. Theroaming process presupposes that an STA moves from AP_A to AP_B.Referring to FIG. 6, the STA transmits an association request to AP_A instep 1. AP_A authenticates the STA in a general initial authenticationprocedure and acquires a security key. The STA already knows an MK usedfor security between the STA and an AAA server (not shown) and receivesa PMK from the AAA server. AP_A receives the PMK from the AAA server.Both the STA and the AP_A then acquire a PTK and an RK (Roam Key). Arandom number (RN) is needed to generate the RK and a 4-way handshake iscarried out using the PMK to generate the PTK. The RN is generatedduring the 4-way handshake. Obviously, the RN may be generated in anyother way. After the authentication, AP_A transmits a response for theassociation request to the STA. Thus, the STA communicates with AP_A.

Meanwhile, AP_A generates a PMK for a neighbor AP, AP_B, managed by itsAP-neighborhood graph. Let the PMK for the neighbor AP be PMK_(next).PMK_(next) is generated using the RK, the current PMK, PMK_(curr), theMAC address of the STA, STA_(mac), and the MAC address of a new-AP, nextAP_(mac) by a PRF (Pseudo-Random Function), expressed asPMK_(next)=PRF(RK,PMK_(curr),STA_(mac,next)AP_(mac))  (1)where STA_(mac) is known to AP_A during communication and next AP_(mac)is information that AP_A receives by the IAPP protocol or from the AAAserver.

In step 2, AP_A transmits PMK_(next) to AP_B. While one AP is assumed asa potential AP in the case illustrated in FIG. 6, if a plurality ofpotential APs exist, AP_A transmits PMKs, PMK_(next) calculated for therespective potential APs to each of them. AP_B stores PMK_(next) in acache. As the STA moves to AP_B in the shown path, the STA requests areassociation to AP_B in step 3. To maintain an on-going communicationservice in response to the reassociation request, a security system mustbe established between AP_B and the STA. That is, a PTK must be gainedfor security between AP_B and the STA. The PTK is derived from a PMK,namely PMK_(next). Hence, AP_B sets PMK_(next) as the PMK by which AP_Bcan communicate with the STA. Meanwhile, the STA can gain PMK_(next) invarious ways. For example, AP_A or AP_B provides the STA withPMK_(next). Or the STA can directly generate PMK_(next) from nextAP_(mac) received from AP_A or AP_B.

As AP_B and the STA acquire the same PMK, the PTK can be created in theconventional method, so that a normal security system can be establishedbetween them. Consequently, the latency involved with the conventionalpre-authentication is reduced, thereby enabling fast roaming andachieving implementation speedups. In the mean time, AP_B generatesPMK_(next) using an RK achieved together with the PTK and transmitsPMK_(next) to its neighbor APs, in preparation for roaming of the STA toany of the neighbor APs.

In the embodiment of the present invention, the security cachingtechnique is adopted to provide a security key used to preserve securitybetween an STA and at least one predicted new-AP to which the STAbecomes associated. Apart from the roaming process, the security cachinginvolves the transfer of the security key from a prior-AP to potentialnew-APs. To implement the security caching technique, potential new-APsfor each AP must be predicted. This has been detailed in relation to theAP-neighborhood graph.

FIG. 7 illustrates a security key generation procedure according to thefirst embodiment of the present invention.

Referring to FIG. 7, the AAA server generates PMK_(curr) for an AP,AP_(curr) that the STA initially attempts to access and transmitsPMK_(curr) to AP_(curr). AP_(curr) acquires a PTK and an RK fromPMK_(curr). The RK is determined using a PRF expressed asRK=PRF(PMK,“Roam Key”,AP_(nonce),STA_(nonce))  (2)where AP_(nonce) is a random number set by AP_(curr), STA_(nonce) is arandom number set by the STA, and “Roam Key” is the RN generated duringthe 4-way handshake.

After the RK is gained by Eq. (2), a PMK for a neighbor AP, PMK_(next)is computed by Eq. (1) and transmitted to AP_(next) by the securitycaching technique. In the presence of a plurality of neighbor APs, asmany PMKs, PMK_(next) as the number of the neighbor APs are generated.

The provisioning of the fast roaming service with a reducedreassociation latency owing to the security caching technique will bedescribed in detail with reference to FIGS. 8A, 8B and 8C. It is to beappreciated that the following description is under the assumption thatthe STA is initially connected to AP_A, and AP_B and AP_E are neighborAPs to AP_A.

FIG. 8A illustrates acquisition of necessary security keys in AP_A andthe STA when the STA initially attempts to access AP_A. The securitykeys the STA acquires are MK, PMK_(curr), PTK_(curr) and RK, while thesecurity keys AP_A acquires are PMK_(curr), PTK_(curr) and RK. Theprocedure for acquiring the security keys has been described earlier andthus its description is not provided here.

FIG. 8B illustrates the generation of PMKs for neighbor APs using thesecurity keys in AP_A and the transfer of them from AP_A to the neighborAPs by the security caching technique. In this example the neighbor APsto AP_A are AP_B and AP_E. PMK_(next) for AP_B (PMK(AP_B)_(next)) isdetermined byPMK(AP_(—) B)_(next)=PRF(RK,PMK_(curr),STA_(mac),AP_(—) B _(mac))  (3)and PMK_(next) for AP_E (PMK(AP_E)_(next)) is determined byPMK(AP_(—) E)_(next)=PRF(RK,PMK_(curr),STA_(mac),AP_(—) E _(mac))  (4)

For roaming that may occur later, the STA must have knowledge ofPMK_(next) corresponding to the neighbor APs. In accordance with thefirst embodiment of the present invention, the STA gains PMK_(next)corresponding to the neighbor APs in two ways, AP_A directly providesthe STA with PMK_(next) delivered to the neighbor APs; and AP_A providesthe STA with MAC addresses needed to calculate PMK_(next) for theneighbor APs. In the latter case, the STA computes PMK_(next) for therespective neighbor APs by Eq. (3) and Eq. (4).

FIG. 8C illustrates AP_B's resumption of a communication service thatAP_A provided, using PMK_(next) after the STA moves from AP_A to AP_B.AP_B translates PMK_(next) received from AP_A into its PMK. If the STAattempts to access AP_B, AP_B derives a PTK from the PMK. Similarly, theSTA acquires the PTK using already known PMK_(next). Thus, the STAresumes the communication service with AP_B, which was provided in AP_A.Meanwhile, AP_B acquires the PTK and an RK simultaneously. Using the RK,AP_B generates PMKs for its neighbor APs managed by its AP-neighborhoodgraph. AP_B transmits the PMKs to the neighbor APs by the securitycaching technique.

Although the case illustrated in FIGS. 8A, 8B and 8C has been detailedon the assumption that the STA roams from AP_A to AP_B, the STA can roamfrom AP_B to AP_A in the same procedure.

FIG. 9 is a diagram illustrating signaling between the STA and the APsin the roaming process according to the first embodiment of the presentinvention. Let AP_A be a prior-AP and AP_B be a new-AP. Since the STAaccesses AP_A and after roaming, the STA operates with AP_B in theconventional manner, the following description is focused on thesignaling for the roaming process.

Referring to FIG. 9, the STA and AP_A derive a PTK and an RK from a PMKreceived from the AAA server (not shown) in step 901 so that they arecapable of communicating with each other. AP_A derives PMKs, PMK_(next)for its neighbor APs in step 903 and transmits the PMKs to its neighborAPs in steps 905 to 907. Thus the neighbor Aps now have the PMKs whichwill be used for security when the STA moves to them.

As the STA roams to AP_B, the STA and AP_B derive a PTK and an RK fromPMK_(next) in step 909, so that STA and AP_B establish a security systemthat allows a communication service from AP_A to be resumed in AP_B.AP_B generates PMKs, PMK_(next) for its neighbor APs in step 911 andtransmits the PMKs to its neighbor APs in steps 913 to 915.

In accordance with the first embodiment of the present invention, theneed for accessing the AAA server for pre-authentication needed toprovide a roaming service for the STA is eliminated, thereby reducingtime required for roaming. This implies that fast roaming is enabled.

3. Second Embodiment

Higher-layer servers manage neighbor APs for individual APs by theirAP-neighborhood graphs. When necessary, the servers generate PMKs forAPs neighboring to a particular AP and transmits them to the neighborAPs. Thus when an STA roams to one of the neighbor APs, a securitysystem operates using the already known PMK, thereby providing fastroaming.

The second embodiment of the present invention presupposes that theAP-neighborhood graphs are managed by a novel higher-layer server, anaccounting server. The accounting server may be incorporated in anexisting AAA server or implemented as a separate server. Also, aplurality of accounting servers can be adopted according to the amountof information regarding the managed AP-neighborhood graphs. It is to beappreciated that the following description is made in the context of anaccounting server implemented independently of an existing AAA serverand this AAA server free of the accounting function is called anauthentication server (AS).

With reference to FIGS. 10A to 10E, fast roaming through security keydistribution from the higher-layer servers will be described in detailon the assumption that the STA initially accesses AP_A, and AP_B andAP_E are neighboring to AP_A.

Referring to FIG. 10A, as the STA initially attempts to associate toAP_A, AP_A and the STA each acquire their necessary security keys. AnMK, a PMK and a PTK are security keys for the STA, while the PMK and thePTK are security keys for AP_A. How the keys are acquired has beendetailed earlier and thus its description is not provided here. Theacquisition of the security keys is equivalent to establishment of asecurity system that allows communication between the STA and AP_A.

Referring to FIG. 10B, AP_A notifies the accounting server of theinitiation of a communication service with the STA, for example by anAccounting-Request message. Thus the accounting server executes anaccounting function for the STA and announces the initiation of thecommunication service between the STA and AP_A to the neighbor APs.

Referring to FIG. 10C, the accounting server searches for the neighborAPs using an AP-neighborhood graph that the accounting server managesfor AP_A, and notifies by a Notify-Request message the neighbor APs,AP_B and AP_E, that the STA has associated to AP_A. The Notify-Requestmessage includes the MAC address of the STA, STA-mac-Addr. Upon receiptof the Notify-Request message, AP_B and AP_E consider that the STA islikely to move from AP_A to them.

Referring to FIG. 10D, the AS provides the neighbor APs (AP_B shown as arepresentative) with PMKs by which they can communication with the STAif and when it roams to them. Specifically, AP_B transmits to the AS anAccess-Request message including STA-mac-Addr received from theaccounting server, and the AS generates a PMK, PMK_(B) for AP_B byPMK_(B)=PRF(MK,PMK_(A),STA_(mac),AP_(—) B _(mac))  (5)where PMK_(A) is a PMK assigned to AP_A, and STA_(mac) and AP_B_(mac)are the respective MAC addresses of the STA and AP_B.

The AS transmits to AP_B an Access-Accept message including PMK_(B). Byreceiving the Access-Accept message, AP_B acquires the PMK to use forsecurity between the STA and AP_B when the STA moves to AP_B. While FIG.10D illustrates an operation between AP_B and the AS, the same thing isalso applicable to AP_E.

Referring to FIG. 10E, a roaming service is provided to the STA as theSTA moves to AP_B. When the STA attempts to access AP_B, AP_B reportsthe access attempt to the accounting server. The accounting server thenupdates an AP-neighborhood graph for AP_B. Meanwhile, the STA acquiresthe PMK, PMK_(B) required to establish a security system with AP_B byPMK_(B)=PRF(MK,PMK_(A),STA_(mac),AP_B_(mac))  (6)where PMK_(A) is a PMK assigned to AP_A, and STA_(mac) and AP_B_(mac)are the MAC addresses of the STA and AP_B. The STA already has theknowledge of PMK_(A) and STA_(mac), while it cannot know AP_B_(mac)without aid from an external device. Therefore, the STA receivesAP_B_(mac) from AP_A, or from AP_B after it moves to AP_B.Alternatively, the STA may receive PMK_(B) from AP_B, instead ofgenerating PMK_(B) directly. This is possible on the assumption thatAP_B has PMK_(B), which has been described earlier.

Once AP_B and the STA know PMK_(B), they can acquire a PTK from PMK_(B)in a known manner. Thus, the method of deriving the PTK from PMK_(B)will not be described here.

In the above-described procedure, the STA and AP_B share the same PTK.This implies that a security system has been established between the STAand AP_B. Therefore, a communication service provided from AP_A can beresumed between the AP_N and the STA.

FIG. 11 illustrates an example of PMK generation when the STA roams in apattern of AP_A, AP_B, and AP_C or AP_D in this order.

Referring to FIG. 11, as the STA initially associates to AP_A, PMK₀ isgenerated in a first generation stage. In a second generation stage, theAS generates PMK_(B) for AP_B from PMK₀ in preparation for roaming ofthe STA to AP_B. As the STA roams to AP_B, the AS generates PMK_(C) forAP_C from PMK_(B) in preparation for roaming of the STA to AP_C in athird generation stage. In a fourth generation stage, the AS generatesPMK_(D) for AP_D from PMK_(B) and PMK_(B) for AP_B from PMK_(C) inpreparation for roaming of the STA to AP_D or AP_B. In a fifthgeneration stage, the AS generates PMK_(B) for AP_B and PMK_(E) for AP_Efrom PMK_(D) in preparation for roaming of the STA from AP_D to AP_B orAP_E.

Sequential generation of a PMK for the next AP from a PMK for theprevious PMK and generation of PMKs for next PMKs from the same previousPMK have been described. Only normal transfer of the PMKs from an AP tothe neighbor APs has been considered in the above description.Nonetheless, erroneous PMK transfer causes no security problems becausea neighbor AP can acquire a PMK in the conventional roaming process whenit fails to acquire the PMK due to the erroneous PMK transfer.

FIG. 13 is a diagram illustrating signaling before the STA roamsaccording to the second embodiment of the present invention. In FIG. 13,an AP that the STA initially associates with is called a first AP, andpotential APs to which the STA may move are called first and secondneighbor APs, respectively.

Referring to FIG. 13, an initial association procedure is carried outamong the STA, the first AP and the AS, as illustrated in FIG. 12 foracquisition of security keys needed for the initial association. In step1301 the first AP notifies the accounting server of the start of acommunication service with the STA by an Accounting-Request messageincluding Acct-Multi-Session-ID and PMK-Generation. Upon receipt of theAccounting-Request message, the accounting server determines whether anAP-neighborhood graph is managed for the first AP and transmits anAccounting-Response message to the first AP in step 1303. At the sametime, the accounting server confirms that the first and second neighborAPs exist for the first AP by the AP-neighborhood graph.

The accounting server transmits a Notify-Request message to the firstneighbor AP in step 1305 and to the second neighbor AP in step 1307. TheNotify-Request message indicates the association of the STA to the firstAP. This message delivers information about Acct-Session-ID,Acct-Multi-Session-ID, and PMK-Generation. By receiving theNotify-Request message, the first and second neighbor APs consider thatthe STA may move from the first AP to them. The first neighbor APtransmits a Notify-Response Message to the accounting server in step1309 and the second neighbor AP transmits another Notify-ResponseMessage to the accounting server in step 1311.

The first and second neighbor APs transmit to the AS an Access-Requestmessage including Acct-Session-ID, Acct-Multi-Session-ID andPMK-Generation in steps 1313 and 1317, respectively.

Upon receipt of the Access-Request message from the first neighbor AP,the AS generates a PMK for the first neighbor AP. In step 1315, the AStransmits to the first neighbor AP an Access-Accept message includingthe generated PMK. The Access-Accept message delivers information aboutAcct-Session-ID, Acct-Multi-Session-ID, PMK-Generation, PMK and Timeout.By receiving the Access-Accept message, the first neighbor AP acquiresthe PMK for a security system which allows secure communication with theSTA after the STA moves to the first neighbor AP.

Upon receipt of the Access-Request message from the second neighbor AP,the AS generates a PMK for the second neighbor AP and transmits to thesecond neighbor AP an Access-Accept message including the generated PMKin step 1319. The Access-Accept message delivers information aboutAcct-Session-ID, Acct-Multi-Session-ID, PMK-Generation, PMK and Timeout.By receiving the Access-Accept message, the second neighbor AP acquiresthe PMK for a security system which allows secure communication with theSTA after the STA moves to the second neighbor AP.

Meanwhile, the STA and the first AP perform typical operations neededfor a communication service between them, such as acquisition of a PTKby 4-way handshake. When the communication service is available, the STAand the first AP transmit/receive communication service data.

FIG. 14 is a diagram illustrating signaling after the STA roamsaccording to the second embodiment of the present invention. In FIG. 14,the STA moves from the first AP to the first neighbor AP and the firstAP and the second neighbor AP are neighbor APs to the first neighbor AP.

Referring to FIG. 14, after the STA moves to the first neighbor AP, itattempts to reassociate to the first neighbor AP by transmitting a ProbeRequest message to the first neighbor AP in step 1401. In step 1403, thefirst neighbor AP transmits to the STA a Probe Response message inresponse to the Probe Request message. The STA transmits a ReassociationRequest RSN IE to the first neighbor AP in step 1409 and the firstneighbor AP transmits a Reassociation Response RSN IE to the STA in step1411.

Meanwhile, the first neighbor AP transmits an Accounting-Request messageto the accounting server to report the reassociation of the STA to thefirst neighbor AP in step 1413. The Accounting-Request message containsinformation about Acct-Multi-Session-ID and PMK-Generation. Upon receiptof the Accounting-Request message, the accounting server updates theAP-neighborhood graph corresponding to the first neighbor AP. Theaccounting server transmits an Accounting-Response message to the firstneighbor AP in step 1415. At this time, the accounting server confirmsby the AP-neighborhood graph that the first AP and the second neighborAP are neighboring to the first neighbor AP.

The accounting server transmits a Notify-Request message to the first APin step 1417 and to the second neighbor AP in step 1419. TheNotify-Request message indicates the association of the STA to the firstneighbor AP. This message delivers information about Acct-Session-ID,Acct-Multi-Session-ID, and PMK-Generation. By receiving theNotify-Request message, the first AP and the second neighbor AP considerthat the STA may move from the first neighbor AP to them. The first APtransmits a Notify-Response Message to the accounting server in step1421 and the second neighbor AP transmits another Notify-ResponseMessage to the accounting server in step 1423.

Upon receipt of the Notify-Request message, the first AP transmits anAccess-Request message to the AS in step 1425. The Access-Requestmessage contains information about Acct-Session-ID,Acct-Multi-Session-ID, and PMK-Generation.

Upon receipt of the Notify-Request message from the first AP, the ASgenerates a PMK for the first AP, for example, referring to theinformation included in the Access-Request message. The AS thentransmits an Access-Accept message to the first AP in step 1427. TheAccess-Accept message contains information about Acct-Session-ID,Acct-Multi-Session-ID, PMK-Generation, PMK and Timeout. By receiving theAccess-Accept message, the first AP acquires the PMK for a securitysystem which allows secure communication with the STA after the STAmoves to the first AP.

Upon receipt of the Notify-Request message, the second neighbor APtransmits an Access-Request message to the AS in step 1429. TheAccess-Request message contains information about Acct-Session-ID,Acct-Multi-Session-ID, and PMK-Generation.

Upon receipt of the Notify-Request message from the second neighbor AP,the AS generates a PMK for the second neighbor AP, for example,referring to the information included in the Access-Request message. TheAS then transmits an Access-Accept message to the second neighbor AP instep 1431. The Access-Accept message contains information aboutAcct-Session-ID, Acct-Multi-Session-ID, PMK-Generation, PMK and Timeout.By receiving the Access-Accept message, the second neighbor AP acquiresthe PMK for a security system which allows secure communication with theSTA after the STA moves to the second neighbor AP.

Meanwhile, the STA and the first neighbor AP perform typical operationsneeded for a communication service between them, such as acquisition ofa PTK by 4-way handshake. When the communication service is available,the STA and the first neighbor AP transmit/receive communication servicedata.

It can be further contemplated as other embodiments that the step ofdetermining whether to apply the inventive roaming technique between anSTA and APs is further performed in addition to the procedures accordingto the first and second embodiments of the present invention. Forexample, the STA notifies whether it supports fast roaming by one ofreserved bits in the RSN IE of a Reassociation-Request message. The APnotifies whether it supports fast roaming by the same bit of aReassociation-Response message. A PMK acquired for the STA can beprovided by the bit.

FIG. 15 is a graph illustrating the results of an experiment thatcompares the conventional roaming scheme (full authentication) with theinventive roaming scheme (re-authentications). As noted from FIG. 15,latency of about 800 ms was observed in the full authentication, whereasthe latency was reduced to 50 ms on an average in there-authentications. Thus the conclusion is drawn that the inventiveroaming scheme supports fast roaming.

As described above, the present invention offers a simplified roamingprocess and so reduces roaming time, resulting in communicationimplementation speedup between an STA and a new-AP in a WLAN. Also,service quality is stably ensured and fast roaming is enabled.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. (canceled)
 2. A method for supporting fast roaming of a mobileSTAtion (STA) in a wireless network including a plurality of neighboringAccess Points (APs) connected to an Authentication Server (AS), themethod comprising: generating, from a master key of the AS, a firstpairwise master key to be shared by the STA and a first AP of theplurality of neighboring APs when the STA attempts to associate with thefirst AP; generating a second pairwise master key from the firstpairwise master key; and providing the second pairwise master key to asecond AP of the plurality of neighboring APs, wherein the second APauthenticates the STA using the second pairwise mater key when the STAattempts to roam to the second AP.
 3. A method for secure communicationsin a wireless network, said wireless network including at least onesever and at least a first access point and a second access point, eachof said first access point and said second access point being capable ofproviding to at least one station an access to said wireless network,said at least one station being capable of roaming from a first networkaccess to a second network access, said at least one station beingprovided with said access to said wireless network by said first accesspoint during said first network access, said at least one station beingprovided with said access to said wireless network by said second accesspoint during said second network access, a first security key beinggenerated in said wireless network during said first network access,said method comprising: sending, by said first access point, a secondsecurity key to said second access point, said second security key basedat least in part on information contained in said first security key,said second key capable of being used by said second access point toaccommodate a fast roaming, in which said second network access can beprovided without acquiring a further security key from said server; andgenerating, by said first access point, a third security key, said thirdsecurity key based at least in part on information contained in saidsecond security key, said third security key capable of being used toestablish a secure communication between said at least one station andsaid first access point.
 4. The method for secure communications in saidwireless network as set forth in claim 3, further comprising: generatingsaid second security key by applying a pseudo random function to a setof information, said set of information including at least saidinformation contained in said first security key and information relatedto an identity of said second access point.
 5. The method of securecommunications in said wireless network as set forth in claim 4, whereinsaid set of information further includes information relating to anidentity of said at least one station.
 6. The method for securecommunications in said wireless network as set forth in claim 5, whereinsaid information related to said identity of said at least one stationincludes a media access control (MAC) address of said at least onestation.
 7. The method for secure communications in said wirelessnetwork as set forth in claim 3, wherein said second security keycomprises a pairwise master key, and said third security key comprises apairwise transient key, each of said pairwise master key and saidpairwise transient key being defined by Institute of Electrical andElectronics Engineers (IEEE)802.11 standard.
 8. The method for securecommunications in said wireless network as set forth in claim 3, whereinsaid second access point is a member of a subset of an extended serviceset, said first access point having knowledge of members of said subset,said subset being updatable to add a new member.
 9. The method forsecure communications in said wireless network as set forth in claim 8,further comprising: sending, by said first access point, at least aversion of said second security key to each of said members of saidsubset.
 10. The method for secure communications in said wirelessnetwork as set forth in claim 8, further comprising: sending a messagethat includes an indication of said first access point being capable ofsupporting said fast roaming.
 11. The method for secure communicationsin said wireless network as set forth in claim 10, wherein said messagecomprises a re-association response message as defined by IEEE 802.11 aspromulgated by Institute of Electrical and Electronics Engineers (IEEE)802.11 standard.
 12. The method for secure communications in saidwireless network as set forth in claim 3, wherein said second securitykey is sent by said first access point to said second access point priorto an initiation by said at least one station of said roaming from saidfirst network access to said second network access.
 13. A method forsecure communications in a wireless network, said wireless networkincludes at least one server and at least a first access point and asecond access point, each of said first access point and said secondaccess point being capable of providing to at least one station anaccess to said wireless network, said at least one station being capableof roaming from a first network access to a second network access, saidat least one station being provided with said access to said wirelessnetwork by said first access point during said second network access, afirst security key being generated in said wireless network during saidfirst network access, said method comprising: receiving, by said secondaccess point, a second security key from said first access point, saidsecond security key based at least in part on information contained insaid first security key; said second key capable of being used by saidsecond access point to accommodate a fast roaming, in which said secondnetwork access can be provided without acquiring another security keyfrom said server; and generating, by said second access point, a thirdsecurity key, said third security key based at least in part oninformation contained in said second security key, said third securitykey capable of being used to establish a secure communication betweensaid at least one station and said second access point.
 14. The methodfor secure communications in said wireless network as set forth in claim13, wherein said second security key received from said first accesspoint includes an information relating to an identity of said secondaccess point.
 15. The method for secure communication in said wirelessnetwork as set forth in claim 14, wherein said second security keyreceived from said first access point further includes an informationrelating to an identity of said at least one station.
 16. The method forsecure communications in said wireless network as set forth in claim 15,wherein said information relating to said identity of said at least onestation includes a media access control (MAC) address of said at leastone station.
 17. The method for secure communications in said wirelessnetwork as set forth in claim 13, wherein said second security keycomprises a pairwise master key, and said third security key comprises apairwise transient key, each of said pairwise master key and saidpairwise transient key being defined by Institute of Electrical andElectronics Engineers (IEEE) 802.11 standard.
 18. The method for securecommunications in said wireless network as set forth in claim 13,wherein said second access point is a member of a subset of an extendedservice set, members of which are known to said first access point. 19.The method for secure communications in said wireless network as setforth in claim 18, further comprising: sending a message that includesan indication of said second access point being capable of supportingsaid fast roaming.
 20. The method for secure communications in saidwireless network as set forth in claim 19, wherein said messagecomprises a re-association response message as defined by IEEE 802.11 aspromulgated by Institute of Electrical and Electronics Engineers (IEEE)802.11 standard.
 21. The method for secure communications in saidwireless network as set forth in claim 20, wherein said second securitykey is received from said first access point by said second access pointprior to an initiation by said at least one station of said roaming fromsaid first network access to said second network access.
 22. The methodfor secure communications in said wireless network as set forth in claim13, wherein said third security key being a pairwise transient keyobtained through a 4-way handshake process between said second accesspoint and said at least one station, each of said pairwise transient keyand said 4-way handshake process being defined by Institute ofElectrical and Electronics Engineers (EEEE) 802.11 standard.